Substrate Coating System

ABSTRACT

The current invention reveals equipment and the method to utilize it to produce coated honeycomb catalyst monoliths as for catalytic converters. This invention utilizes two chambers, the first to contact the substrate with a washcoat, the second to ensure removal of coating solution from the interior of the substrate. The first coating chamber uses a precisely controlled volumetric application from below ensuring complete internal contact with no overflow from the top of the substrate. Removal of excess washcoat is volumetric, providing a relatively high pressure differential across the substrate to effectively remove all of the excess washcoat from the substrate. The second chamber provides a higher differential pressure through a similar mechanism, preferentially with the substrate inverted. Washcoat removed from the substrate in chamber two impinges on water, and is re-introduced to chamber  1  through the seal cleaning mechanism. Fresh make up water is supplied to chamber  2  to replenish water removed to the seal cleaning system. After each washcoat contact with substrate in chamber  1,  a precise replenishment of the washcoat in the retained washcoat solution is made, this quantity providing precisely the desired concentration of washcoat on the substrate. Any lost volume in chamber  1  coating solution is adjusted with water from chamber  2  as required. The unique nature of the invention minimizes and in some cases avoids issues common to existing technologies. These include consistent washcoat mean loading, even washcoat distribution regardless of selective adsorption due to particle size, even distribution of washcoat throughout the substrate interior, uncoated exterior, and greatly reduced waste water production.

Substrate coating is used in the catalytic converter production industry, coating the interior of honeycomb monoliths with inorganic compounds and precious metals. The process of coating these substrates takes a number of forms, noted by prior knowledge. Washcoat has been injected into individual cells within the substrate, with a typical method using pressure and vacuum to evenly coat the cells. Limitations of these processes are variability of coating compositions due to depletion of the coating solutions, uneven distribution from measured introduction, waste water production, and precious metal losses through air borne means, waste water and precipitation in processing equipment. The current invention reveals a process that minimizes the quantity of material in process at any time, effectively recycling to the coating chamber all materials added to the process thereby assuring that the coating composition on each part is identical. The process also allows precise control of partial substrate coating, allowing the user to produce a single substrate with multiple coating chemistries along the linear path of the pores.

The invention described here provides a superior application of washcoat to substrates. The current employment of the invention is in the catalytic converter coating industry, and is directly applicable to any industry where a measured uniform solution or suspension coating is desired onto the interior surface of a honeycomb material. Referring to FIG. 1, a substrate (7) is placed in the coating chamber (2), such that the substrate is held at or near the bottom of the solid surface of the substrate by a seal (1). The bottom of the coating chamber is defined by a flexible diaphragm (3), with a pulse chamber (4) with a confined volume of non-compressible fluid contained in the pulse chamber. A precise quantity of coating material (5) is introduced into the coating chamber, as measured by the level indicator in the coating chamber (8). A volumetric pump (6), in one embodiment a variable stroke piston pump, operates to introduce a finite volume of a non-compressible fluid into the pulse chamber below the coating deflecting the diaphragm inward a fixed volume toward the coating chamber. This results in a precise level of washcoat being introduced into the substrate, an amount that results in the washcoat covering the entire interior of the substrate without overflowing the substrate, and in some cases filling the substrate to only the level required to coat a portion of the substrate. This is accomplished by precisely controlling the diaphragm movement and the volume in the coating chamber prior to deflection. During the retraction phase of the coating process, the volumetric pump operates in reverse, pulling against the diaphragm, creating a controlled vacuum to assist in washcoat removal that continues to the fully retracted position of the diaphragm. The seal holding the substrate is released, the substrate is removed from the coating chamber, and is placed in the suction chamber. The washcoat makeup pump operates to replenish the mass of washcoat in the coating chamber by the precise target quantity in the substrate. The volume of solution in the coating chamber is measured, and dilute solution from the suction chamber is introduced in any manner to bring the level up to the desired control level. The process in the coating chamber is repeated. After repeated cycles, a stable steady state of coating density is achieved. The coated substrate is placed into the suction chamber, identical in mechanical design to the coating chamber, with the seal holding the substrate in a manner similar to the coating chamber. A level of dilute solution is maintained in the suction chamber in close proximity to the bottom of the substrate, generally providing between 0 and 1 substrate volumes of air space between the solution and the substrate. The moveable bottom surface, in this instance a diaphragm similar to the coating chamber, is deflected in the same manner as the coating chamber in such a way as to produce a pressure differential through the substrate to remove any entrained washcoat from the interior of the substrate. Removed washcoat impinges onto the solution in the suction chamber. The seal is released and the substrate removed. The moveable bottom surface is returned to its full up position, and the liquid level is measured. Makeup solution, water in the case of aqueous solutions, is added to return the level to its controlled level. In this process, all coating materials that are introduced into the coating process are contained in the coating and suction chambers, with the mass of introduced makeup solution is contained within the substrate leaving the suction chamber. Predictive selective adsorption can be used to modify the initial coating chamber chemistry. In practice, the coating solution chemistry in the coating chamber stabilizes after several substrates are coated.

Preparation of zones within catalytic converter substrates for sequential gas treatment is possible with this improvement. Currently, stacks of individually coated catalysts are assembled to provide this zone treatment. With this improvement, using partial filling of the substrate, zones can be created within the substrate to provide the same effect with one substrate, eliminating the need to stack thin substrates. 

1. In a manufacturing process where it is desired to introduce materials in solution or suspension onto the interior surfaces of a substrate, the improvement consists of a coating system which is comprised of: a. a cylindrical coating chamber having a chamber wall with an interior facing surface defining an interior space, at least one interior seal positioned within the wall having a seal face arranged to face the interior space within the chamber, the seal capable of securing the bottom lateral face of a substrate, and an impermeable moveable bottom interior wall, with an interior facing surface, such that the interior volume defined by the chamber wall, interior seal and bottom interior wall can be varied; b. a cylindrical coating pulse chamber having a chamber wall with an interior facing surface defining an interior space, an impermeable interior facing moveable top interior wall, the exterior of said moveable wall being the moveable bottom interior wall in a coating chamber, and a bottom surface provided by a volumetric pump, where the interior volume described by the pulse chamber is confined in volume with an incompressible fluid, such that action by the volumetric pump moves the moveable top interior wall to vary the volume described by the coating chamber; c. a metering system supplying coating solution to the coating chamber; and d. a level indicator measuring the solution level within the coating chamber.
 2. The device in claim 1, wherein the interior surface described by the cylindrical walls of the coating chamber is formed by two truncated cones, the upper cone inverted, joined at the minimum radius.
 3. The device in claim 1, wherein the moveable interior wall of the coating chamber is a flexible diaphragm secured at the cylinder wall.
 4. The device in claim 1, wherein the non-compressible fluid in the coating pulse chamber is isothermal degasified water.
 5. The device in claim 1, wherein the seal is an inflatable flexible seal.
 6. The device in claim 2, wherein the level indicator is positioned such that the level is measured at the minimum radius of the joined truncated cones.
 7. The device in claim 1, wherein the base of a catalyst substrate is secured by the seal and the coating chamber moveable surface is displaced into the coating chamber interior space by action of the volumetric pump through the coating pulse chamber, thereby reducing the coating chamber interior space and forcing solution into the substrate.
 8. The device in claim 7, wherein the volume of solution forced into the substrate is controlled by the operation of the volumetric pump to regulate the volume and rate of solution introduced into and removed from the substrate.
 9. In a manufacturing process where the interior surfaces of a substrate have been coated with an excess of materials in solution or suspension, and it is desired to remove that excess solution or suspension, the improvement consists of a suction system which is comprised of: a. a cylindrical suction chamber having a chamber wall with an interior facing surface defining an interior space, at least one interior seal positioned within the wall having a seal face arranged to face the interior space within the chamber, the seal capable of securing the bottom lateral face of a substrate, and an impermeable moveable bottom interior wall, with an interior facing surface, such that the interior volume defined by the chamber wall, interior seal and bottom interior wall can be varied; and b. a cylindrical suction pulse chamber having a chamber wall with an interior facing surface defining an interior space, an impermeable interior facing moveable top interior wall, the exterior of said moveable wall being the moveable bottom interior wall in a coating chamber, and a bottom surface provided by a volumetric pump, where the interior volume described by the pulse chamber is confined in volume with an incompressible fluid, such that action by the volumetric pump moves the moveable top interior wall to vary the volume described by the coating chamber.
 10. The device in claim 9, wherein the interior surface described by the cylindrical walls of the suction chamber is formed by two truncated cones, the upper cone inverted, joined at the minimum radius.
 11. The device in claim 9, wherein the moveable interior wall of the suction chamber is a flexible diaphragm.
 12. The device in claim 9, wherein the non-compressible fluid in the suction pulse chamber is isothermal degasified water.
 13. The device in claim 9, wherein the seal is an inflatable flexible seal.
 14. The device in claim 9, wherein the level indicator is positioned such that the level is measured at the minimum radius of the joined truncated cones.
 15. The device in claim 9, wherein the coating chamber moveable surface is displaced from the coating chamber interior space, by reversing the volumetric pump through the coating pulse chamber, thereby increasing the coating chamber interior space and creating a vacuum in the suction chamber, pulling solution from the substrate into the coating chamber at a rate capable of removing entrained solution from the interior surfaces of the substrate, the removed entrained solution impinging onto the solution in the suction chamber.
 16. The device in claim 1 and the device in claim 9, wherein the two are connected in series with a solution transfer system to recycle the recovered entrained from the suction chamber device in claim 9 to the coating chamber device in claim
 1. 